The blast, which caused damage to water pipes and smashed windows, appeared to be timed to coincide with the gathering of riot police ahead of a bullfight. Twenty-six people, mostly police, were injured.

Villegas told local W Radio the device was probably activated remotely by a cellular phone and that suspects have been identified.

If proved to be the National Liberation Army (ELN), the attack will anger President Juan Manuel Santos who is engaged in peace talks with the rebel group in Ecuador.

The ELN, which has about 1,500 combatants have stepped up attacks on economic infrastructure since talks began this month. There have been two bombings of an oil pipeline in less than a week and the kidnapping of an elderly man.

Santos is seeking to end a war with the ELN, which has battled dozens of governments since it was founded five decades ago.

The Revolutionary Armed Forces of Colombia (FARC), the biggest rebel group in the South American country, signed a peace accord late last year and is currently preparing to turn in its weapons.

It was initially assumed that the attack was in relation to the bullfight. Hundreds of protesters have gathered weekly to demonstrate against bullfighting in Bogota, which resumed last month for the first time after being banned four years ago.

The ban was lifted by the Constitutional Court, which said it was part of the national heritage, prompting weekly clashes with police.